Method and device for the heating of material in electric furnaces



Apr. 3, 1923. 1,450,543

E. A. A. GRONWALL METHOD AND DEVICE FOR THE HEATING OF MATERIAL IN ELECTRIC FURNACES Fi 18d Sept 28, 1921 ATTX Patented Apr. 3, 1923.

UNITED STATES PATENT OFFICE.

EUGEN ASSAR ALEXIS GR6NWALL, 0F STOCKHOLM, SWEDEN.

METHOD AND DEVICE FOR THE HEATING OF MATERIAL IN ELECTRIC FURNACES.

Application filed September 28, 1921. Serial No. 503,792.

To all whom it may concern:

Be it known that I, EUGEN AssAR ALEXIS GR6NWALL, subject of the King of Sweden, residing at Stureplan 13, Stockholm, Sweden, have invented new and useful Improvement in Methods and Devices for the Heating of Material-in Electric Furnaces, of which the following is a specification.

Electric furnaces. for heat-treatment of materials for instance reheating or annealing of metals or other materials have previously been constructed on the following principle: The electric current is supplied to a resistance string bonifero'us material, placed on a bed of carborundum, for example of carborundum bricks, or in open channels of carborundum. When the electric current has for some time passed throu h the graphite string, the bed of carborun um gets so heated that it becomes electrically conductive, so that the current passes both through the graphite string and through the carborundum bed or carborundum brick. This process, however, has proved to be attended by great drawbacks in view of the fact that the carboniferous material or graphite gets consumed: whence it has been found necessary to add fresh supply of graphite, or else considerably to increase the tension, in order to cause the current to pass chiefly through the carborundum brick serving as a bed.

The present invention relates to a process and device whereby this drawback is obviated. In accordance therewith, the electric furnace is supplied with current through pipes of carborundum, siloxicon, or similar refractory material, containing silicon-carbide, in which pipes, previous to the counecting-up of the electriccurrent, there has been placed or arranged a string, or a continuous layer, of graphite or other carboniferous material, which is able in a cold state to conduct the current. Owing to the fact that the carbon or graphite is enclosed in the pipes, the air can be excluded. Consequently the graphite or carbon is not consumed. As soon as the pipe has been sufficiently heated by closing the circuit through the graphite, the graphite string is broken in some way, and the current is induced to pass entirely or chiefly through the walls of the carborundum pipe. The breaking of the graphite string may be effected in several different ways. If the of graphite or car-' graphite string consists of grains, the current can be interrupted by pushing the electrode in connection with the source of electricity some little distance into the pipe and then withdrawing it, or else the carborundum pipe may be arranged rotatably around its axis, so that the graphite grains can be separated by turning the pipe and the current thus interrupted. The graphite string may also be formed of a thin graphite rod, which is removed when the carborundum pipe has been suflicientl'y heated. The pipes may of course be of any shape, or cross-section, for example round or square, etc., and each pipe or tube may be made in one piece or composed of several pieces.

The carborundum pipes may be placed either in the furnace chamber proper or under the bottom of the furnace, or may be built into the actual masonry in a horizontal, vertical or sloping position. It may be found convenient: to couple the graphite strings or the carborundum pipes in such wise that one or more pipesor groups of pipes are coupled alternately in series or parallel.

In order to make plain the invention there is shown on the accompanying drawing, by way of example, a reheating furnace performed in accordance with the invention, in cross section. The actual furnace may be similar in appearance to an ordinary reheating furnace worked by gas, but obviously without a gas generator, whence no further description or drawing may be necessary in order to show the appearance of the furnace from the above or from the side.

In the drawing, 1 designates the masonry her proper, which may be constructed in the ordinary manner,

covered at the top by an arch or roof 3. 4 designates one of the discharge openings arranged in the ordinary manner, which during the process are held closed by a shutter 5. 6 designates one of the pipes arranged in accordance with the present invention, serving for the electric heating, and 7 designates the auxiliary resistance mass arranged in said pipe, consisting of strings, grains, or the like, of graphite or other carboniferousmaterial, for example pieces of carbon electrode material of the size of a nut; The electric current is supplied to or carried off from the pipe 6 through the electric connections 8, which are in electric communication with the hollow current to pass through electrodes 9 of carbon, graphite, or other suitable material, which in the manner indi cated in the drawing, 'With their inner suitably eventually beveled ends 10 rest against the ends of the pipe 6 bevelled in a corresponding manner, so as-to attain a satisfactory transmission of current from the electrodes 9 to the pipe 6. In order in startin upwhile the walls of thepipe 6 are stil cold and thus non-conductive or very badly conductive-to ensure the transmission of current from the electrodes 9 to the resistance mass 7 in the pipes, auxiliary electrodes 11 may be employed, these latter may consist, for example, of short graphite electrodes 11 which are introduced through the openings 12 in the electrodes 9, and the end surfaces of which rest against the resistance mass 7. While the side surfaces rest against the inner Walls of the electrodes 9 and the pipe 6, for which purpose. the auxiliary electrode is placed just over the joint between the pipe 6 and the electrode 9.

. The electric current thus passes, on starting up, from the carbon electrode 9 to the auxiliary electrode 11, and from the latter throu h the carbon pieces or the resistance mass in the pipe, and at the other end of the pipe from the resistance mass 7 through the auxiliary trode 9. When the carborundum plpe has been heated to redness, it becomes electrically conductive.

Having thus described my invention I declare that, what I claim is: y

1 Process for heating an electric furnace, which consists in passing a current through a conductive resistance to heat a pipe of refractory material non-conductive When cold to a temperature where it becomes conductive, causing the current to pass through said material, and reducing the conductivity of the said resistance;

2. Process for heating an electric furnace, which consists in enclosin graphite in a pipe of refractory materia non-conductive when cold, passing a current through the graphite to heat said pipe to a temperature where it becomes conductive, causing the said heated pipe,

electrode to the carbon elecand diffusing the graphite to reduce the conductivity thereof.

3. An electric furnace comprising. refractory pipes, auxiliary resistances of carbons iferous material disposed in said pipes, and a pair of electrodes in cont-act with said L An electric furnace comp-rising refractory pipes, auxiliary resistances of carboniferous material disposed in said pipes,a pair of hollow electrodes in contact with said pipes, and an auxiliary electrode in each of said hollow electrodes and extending into said pipes for ensuring a satisfactory transmission of current from the electrode to said auxiliary resistances.

5. An electric furnace comprising rotatable pipes of refractory material, a layer of graphite disposed in said pipes, and a pair of electrodes in contact with said pipes and graphite.

6. An electric furnace comprising, refractory pipes, carboniferous material disposed in said pipes, a pair of hollow electrodes in contact with said pipes and said carboniferous material, and means for increasing the resistance of said carboniferous material I so as to cause the current to pass mainly through the refractory pipes.

7. An electric furnace'comprising carborundum pipes, posed in said pipes,

carboniferous materia a pair of hollow elec- EUGEN ASSAR ALEXIS caouwui.

Witnesses:

AUG. HAGELIN, E. MILoN'.

1 distrodes in contact with said pipes and said 

